Method for fabricating self-aligned contact hole

Details Method for fabricating self-aligned contact hole Method for fabricating self-aligned contact hole

1999-04-02

2001-10-16

Bowers, Charles (Department: 2813)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S233000, C438S303000, C438S622000, C438S595000, C438S696000, C438S700000

Reexamination Certificate

active

06303491

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for fabricating semiconductor devices, and more particularly to a method for fabricating a self-aligned contact hole suitable for dynamic random access memory cells (DRAM).
2. Description of the Prior Art
Referring to
FIGS. 1A through 1I
, the cross-sectional side views of a conventional method for fabricating a self-aligned contact hole are depicted in sequence.
Referring now to
FIG. 1A
, a cross-sectional view of the first step is schematically shown. In
FIG. 1A
, a polysilicon layer
14
, a polycide layer
16
, a silicon nitride
18
, and a silicon oxide
20
are sequentially formed by chemical vapor deposition on a silicon substrate
10
having a conductive region
12
, for example a source/drain region. The silicon nitride layer
18
has a thickness of approximately 2000 Angstroms, and the silicon oxide layer
20
has a thickness of approximately 500 Angstroms.
Next, as shown in
FIG. 1B
, the silicon oxide layer
20
and silicon nitride layer
18
are etched to expose the upper surface of the polycide layer
16
.
Then, as shown in
FIGS. 1B and 1C
, using the remainder silicon oxide layer
20
and the silicon nitride layer
18
as the etching mask, the polycide layer
16
and the polysilicon layer
14
are etched by anisotropic etching to form a trench
21
which exposes the conductive region
12
.
Referring now to
FIG. 1D
, a silicon nitride layer
22
is deposited on the bottom and sidewall of the trench
21
by chemical vapor deposition.
As shown in
FIG. 1E
, the silicon nitride layer
22
is etched back to form a first nitride spacer
22
a
thereby exposing the conductive region
12
. At the same time, the silicon oxide layer
20
is removed.
Referring now to
FIG. 1F
, a borophosphosilicate glass (BPSG) layer
24
is filled into the trench
21
, extending the upper surface of the silicon nitride layer
18
. Then, a photoresist layer
26
is formed in a predetermined position by using photolithography process.
Next, as shown in
FIGS. 1F and 1G
, a part of the BPSG layer filled in the trench
21
is removed using the photoresist layer
26
as the etching mask, thereby forming a self-aligned contact hole
27
which exposes the conductive region
12
. Afterward, the photoresist layer
26
is removed. In order to completely expose the conductive region
12
, a part of the first nitride spacer
22
a
and the silicon nitride layer
18
would be removed too.
Afterwards, referring to
FIGS. 1G and 1I
, a silicon nitride layer
28
is formed by chemical vapor deposition. Then, the silicon nitride layer
28
is etched back to form a second nitride spacer
28
a,
thereby achieving a better insulating effect.
However, the conventional self-aligned contact hole process suffers from problems. For example, the narrow slit of trench
21
containing first nitride spacer
22
a
can cause the etching step of silicon nitride layer
28
to stop (as shown in FIGS.
1
H and
1
I).
Moreover, in order to serve as the etching stop layer, the silicon nitride layer
28
must have a larger thickness, for example 2000 Angstroms. Therefore, the thermal budget will be increased.
SUMMARY OF THE INVENTION
In view of the above disadvantages, an object of the invention is to provide a new method for fabricating a self-aligned contact hole.
The above object is attained by providing a method for fabricating a self-aligned contact hole comprising the steps of: (a) sequentially forming a conductive layer, a silicon oxide layer, and a first silicon nitride layer on a semiconductor substrate having a conductive region; (b) selectively etching said first silicon nitride layer, said silicon oxide layer, and said conductive layer to from a trench, thereby exposing said conductive region; (c) forming an oxide layer over said first silicon nitride layer, said oxide layer filling into said trench; (d) defining a photoresist layer which has an opening in a predetermined position; (e) removing said oxide layer filled into said trench to form a self-aligned contact hole by using said photoresist layer as the masking layer; (f) removing the photoresist layer; and (g) forming a silicon nitride spacer on the sidewall of said self-aligned contact hole.
An aspect of the invention is to provide a method for fabricating a self-aligned contact hole in which said oxide layer in step (c) is a borophosphosilicate glass (BPSG) layer. Furthermore, the first silicon nitride layer has a thickness of somewhere between 400 and 900 Angstroms, preferably between 500 and 600 Angstroms.


REFERENCES:
patent: 5728595 (1998-03-01), Fukase
patent: 5863820 (1999-01-01), Huang
patent: 6001541 (1999-12-01), Iyer
patent: 6043116 (2000-03-01), Kuo

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